Welcome, everyone to 100 Climate Conversations and thank you for joining us. Today is number 51 of 100 conversations taking place every Friday. The series presents 100 visionary Australians that are taking positive action to respond to the most critical issue of our time: climate change.

Before we begin, and on behalf of the Powerhouse, I’d like to acknowledge the Traditional Custodians of the ancestral homelands upon which this museum is situated, the Gadigal people of the Eora Nation and pay my respects to their Elders past and present.

We are recording live today in the Boiler Hall of the Powerhouse museum. Before it was home to the museum it was the Ultimo Power Station. Built in 1899 it supplied coal powered electricity to Sydney’s tram system into the 1960s. In the context of this architectural artefact. We shift our focus forward to the innovations of the net zero revolution.

My name is Yaara Bou Melhem. I’m a journalist and documentary film director and I often make public interest films at the intersection of art and science. With me today is Vivian Tam, a construction engineer and academic who is one of the co-inventors of CO2 Concrete, which uses a new method of injecting carbon dioxide into recycled aggregate to improve the bonding process, diverting waste from landfill and lowering emissions. Vivian is an associate dean in the School of Engineering, Design and Built Environment at Western Sydney University. We are so thrilled to have her join us today. Please join me in welcoming Vivian Tam.

Vivian, let’s start with the basics, concrete. It’s not something that is usually seen as problematic to the average person, especially in the context of climate change. Why is concrete your focus?

Yes, because I’m focusing on construction management or construction engineering, under the construction and demolition waste, 80 per cent of that waste actually comes from masonry waste. And that means a lot of it is actually concrete. I’ll give you a [few] more figures to understand the details. Every year in Australia about 22.5 million tonnes of C and D waste, construction and demolition waste, [is] produced in Australia. Roughly around 5.5 million tonnes of concrete waste are actually generated. But unfortunately we have this wastes, about 5.5 million tonnes of concrete waste, but this year less than 5 per cent were recycled and less than 1 per cent was actually recycled as concrete applications. That is why I like to focus on concrete, because I can see if I can reuse it properly, that actually can cover a majority of those C and D wastes.

And on a macro level, I suppose if you’re talking about what impact the production of concrete has on global emissions, could you tell us a little bit more about that?

In the global perspective, 5 to 8 per cent of the carbon dioxide emissions actually come from cement and concrete productions. That’s why you can see the majority of our activities we are required to use cement and concrete for the construction. That’s why this is about 5 to 8 per cent of those global emissions that are from the cement and concrete productions.

Tell us about when you studied and started your career in Hong Kong, how that shaped your understanding of the construction industry.

You are talking about roughly about 20 years ago now, after I finished my undergraduate, I started my PhD straight away. But with the concrete waste that I am looking into, you can imagine that Hong Kong is a very densely populated city, and you don’t really have space at all. You can see everywhere when you’re walking along the street, waste is everywhere. And buildings, just building next to it but the waste could be right next to it, and you don’t know how to deal with it. And I was thinking about why [does] the waste have to be there? Why do they want to put the waste next to the building that they’re building? They just cannot get rid of it, or they just have to find a way to send a landfill. What if we can just go straight back to the building? And that is what my research passion come from. I just like to see waste into resources. It’s just a matter of how you think that is the waste They are actually not waste, it depends on whether you can understand their value.

You’re the co-inventor of CO2 Concrete. A new process for producing durable and high strength recycled concrete. Can you tell us about CO2 Concrete and how it is a solution to the impacts we’ve just discussed?

Yes, because when the building is crushed, they have recycled aggregate or concrete waste they produce and that’s why they crush it as a recycled aggregate. But the problem of the existing recycled aggregate is they will attach with the old cement mortar which brings the behaviour down, the properties down, the strength down and also the durability down as well. Just by reusing those recycled aggregate into the recycled concrete, the strength also goes down. It is roughly about 30 per cent strength reduction with 100 per cent recycled aggregate replacement.

As I mentioned, the recycled aggregate has to cement mortar, attach on a weak portion, by injecting carbon dioxide in it actually strengthens those weak parts into the strong part. That means the recycled aggregate is not like the old, recycled aggregate anymore. They strengthen the old cement mortar to become like the good old aggregate. And then that’s why we can reuse it for other purposes. By injecting it with carbon dioxide into the recycled aggregate, the strength actually goes back up. I mentioned about 30 per cent strength reduction. The strength actually goes back up, matching with the virgin concrete behaviour. At the moment, the carbon we are purchasing from the existing market, we understand that the existing market is using a carbon capture technology. That means they are actually capturing the carbon from the atmosphere and then they sell it in the bottle for us. We are relying on the carbon suppliers and there’s plenty of them [that] are doing it right now.

How does CO2 Concrete compare in terms of its carbon footprint to virgin concrete, to the production of the concrete that we usually use?

That’s a big difference. That is also where the benefits come from as well, because we are reusing the carbon dioxide and also we’re reusing the concrete waste that no one want to produce a CO2 Concrete. In the lifecycle carbon emission perspective, it is roughly about 75 per cent of the virgin concrete production is only required for the CO2 Concrete. If we are further reducing the cement adoption, that means we are using some of the cement substitute materials, the lifecycle carbon emission could be about 50 per cent of what virgin concrete will have for the CO2 concrete.

And so, walk us through how CO2 Concrete is made. Where does the waste concrete come from and where is the CO2 that it’s injected with come from?

Construction processes like that is, we have a building up to a certain level of lifetime. You will need to demolish it and then they will crush it and then it will become recycled aggregate. They normally do this at a centralised recycling plant. They have the facilities to crush it as recycled aggregate normally about 20 or 10mls size and once you have those recycled aggregate, normally they can be directly reused as different purposes. But the CO2 Concrete I would need to pre-treat to recycled aggregate. That means in the central recycling plants they already have the recycled aggregate produced. What I do is I inject carbon dioxide in the process, right before they send the aggregate out. That is the pre-treatment that we have. Once we have done the pre-treatment, the rest of the process is exactly the same as what you would do for any other concrete.

So, can you continually recycle CO2 Concrete, or do you need to rely on virgin concrete being available in order to do what you do?

CO2 Concrete can be completely recycled because the process is very simple. It is very pure as well. Just really by injecting carbon dioxide, there’s nothing else, nothing really tricky at all to put it into the concrete. That’s why we can – we produce the recycled concrete back to where it can be like a virgin concrete, because I am just purely injecting carbon dioxide in. They are not only about closing the loop – that means it’s not only about you reusing the product to where it was – I can actually also bring that circular economy back. That means you can have to keep recycling it forever because there’s nothing else. And unless you have different kind of chemicals in, then you may need to be a bit more concerned, but for the CO2 Concrete, they can just recycle forever.

So, could you tell us about this sort of circularity in the construction industry and how CO2 Concrete could help close the loop?

Yes, I understand that there’s a lot of different technologies that are available in the market. They can close the loop, they can bring the products back to life, they can add a lot of different chemicals in, they can actually bring their strength back up. Some industry maybe even adds additional cement in to subsidise the strength reduction to bring that back to life as well.

But to me, I don’t feel like that is really comparable because you’re not comparing apples to apples, you are comparing two different products at the end of the day. I just like to purely replace what we believe are the weak products and replace it with a stronger product. That’s why it’s not only about closing the loop. And also using it as a natural way as well. That means you wouldn’t just naturally put the carbon dioxide, If I don’t inject the carbon dioxide, they actually still have the natural carbon absorption in the atmosphere. It’s just a matter of how fast it is. What my process is doing is accelerating the process, that means it could be for 50 years ahead. I’m just fast tracking it, putting more carbon in for a good reason, to bring the strength back up.

How difficult is it for you to actually source waste concrete? [Are] there incentives for construction companies and builders to actually send concrete to recycling plants, or is it cheaper just for it to go to landfill?

In Australia most of the space, is similar the pricewise it is a little bit different. Because the sending to landfill charge is higher than sending it to the recycling plant charge. That’s where the incentives come from. Because they have enough incentive to help them to do a bit of sorting to put the clean concrete waste to the recycling plants. Rather than [being] charged a bit higher for the landfill cost. And they believe that that is the balance that they have and that that is also the incentive that you have mentioned as well.

That’s good, so you have the source for the concrete and CO2 as we know, is in abundant supply. Let’s now go to applications of CO2 Concrete, because vigorous testing is required for new materials that form the foundations of our buildings and infrastructure. How have you been testing CO2 Concrete?

Yes, this particular research started in 2016. It is about seven years ago now, roughly. We started with very small laboratory scales and after a couple of years we had actually done all the tests, all the material tests that you would imagine. All the physical and mechanical properties like strengths test, durability test, and also some of the shrinkage and also the permeability behaviour. We’ve done all those tests and we believe that the product is ready. And we also know that the long-term performance as well, not only that the strength is good, but also durability.

And that’s where the laboratories work doing in the past couple of years. And once we see that, we know that we need to show it to the market, that we can use it. Because the laboratory we are only making cylinders. And what is that difference? And what is it like? How can we use it at the industry point of view? We were talking to the university, and we are able to pour some small-scale slabs. The first one is back in 2019, April. It is relatively small, I think 30 centimetres by 50 centimetres. And then in 2019, March we actually extended that to three metres by three metres slabs. At that time, we also required support from industry as well. And of course, Covid hits. And then we stopped for a while until last year.

So, what is your measure of success. Is it that CO2 Concrete is comparable or even better than virgin concrete?

Definitely. I believe from that experimental work we can see CO2 Concrete is reusing all those recycled products and the strength is still there. As I mentioned, the strength is lowered by 30 per cent just buy purely replacing recycled aggregate. But the strength that you get back up is after the injecting of carbon dioxide. And that’s what CO2 Concrete is, it is as durable and as strong as virgin concrete.

And with the tests that you so far conducted, for instance, that slab, the three by three metre slab that you just mentioned, have you been able to track what has happened?

Of course, yes. We are actually doing some kind of monitoring for them. We actually check them every month and see whether they are still behaving obviously by visual but also, we are doing some rebound hammer tests to check that whether the strength is still where it was as well. 2019 until now is four years now, and we didn’t see any changes.

So, it is behaving the way you would like it to, or the way has been behaving in the laboratory?

It is, yes. I would also like to mention that the application of those three metres by three metres slabs are actually [being] used as an underneath slab for animals for drinking water. Normally – because one of our campuses is in Hawkesbury, they are actually a farm, and they have different kind of animals as you can imagine. This is the farm where they have all the bulls and cows, and you can imagine how they drink water. They have a cow drinking station in there, but the grass is underneath and when they drink water, they make a whole mess out of it with the water around and the grass around. That’s why the university was thinking about putting slabs underneath the cow drinking station. This means I have a slab underneath, the cow drinking station on top. The cow and the bulls stand there to drink the water. Each bull is about one tonne of weight and that particular slab we can put about six bulls and that is a weight test for the slabs. And after four years the slabs are still working well.

That’s a pretty organic way to test weight on the slab. Put six bulls, six tons that’s pretty amazing and they just what, come on and off all the time because that’s where the troughs are and that’s where they want to drink. What is the next stage of testing? Is there a goal for it to be used in as many applications as traditional concrete?

Definitely, yes. My dream is to really use the product anywhere we can and that is why we are also joining the Holcim Accelerator program. Last year, back in May 2022, we were very lucky enough to be selected as the winner for the Australian challenge in the Holcim Accelerator program and there’s only nine startup companies which have been selected globally. And Australia has only selected CO2 Concrete. And I [was] doing this six-month program last year. One of our main targets is to pour demonstration slabs and that’s where we have been able to produce the demonstrating slabs, 26th of October 2022 is a very special day for me.

And what about other applications? So, for instance, now you’re looking at slabs. What about other elements of building and construction, infrastructure and more foundational elements?

Yes, we are actually looking into additional testing and confirmation just to provide a confidence that industry needs. We are extending to structural behaviour and also fire behaviour to test CO2 Concrete just to ensure that CO2 Concrete can work everywhere, that it can for virgin concrete. And ultimately, you’ll be living in a house, with only CO2 Concrete around you.

And what have initial tests come back with in terms of some of those more foundational elements and moving from slab to say pillars and columns and roof slabs.

At the initial stage we didn’t see too much difference, which is really great. And that’s what we are hoping to have a comprehensive picture, to understand that we are 100 per cent right.

You’ve said before that many in your field are a little bit resistant in the construction industry, or at least very slow to change. How difficult do you think will it be to roll this product out into the industry?

I think it’s still very hard from my point of view, despite the research done for seven years already. I believe the products can work anywhere. It can work for concrete. But the thing is, industry is still really conservative because – although they are trying to pour more laps in the university and also outside the university. But the thing is, they will say we didn’t know what will happen in the future. They will say why do they need to be the first one to be using the CO2 Concrete. They believe in it. They like the idea. They can see that the benefits of it. But the thing is, why do they need to be the first one? That is still the conservative thinking that the industry has, and I think it still has a bit of a way to go. And I am really looking forward to seeing any construction industry partners that are interested to really join venture with the production of CO2 Concrete, so we can work on that together.

So, there’s obviously the sustainability components of CO2 Concrete as being attractive to the market perhaps in order to get people to use it. But what about the price point? Is it the same? Less? More expensive than traditional concrete?

Because recycled aggregate is naturally about half price of the virgin aggregate, which is the market price at the moment. Anyone can buy in the market from the central recycling plants. Because they are half the price of the recycled – compared to virgin aggregate. Those I’m injecting carbon dioxide and different kind of labours involved in the carbonation processes. The CO2 Concrete with 100 per cent aggregate replacement is still roughly about 10 per cent cost reduction compared to virgin concrete. As you know, everyone needs to use concrete. If we start by a small component, we start saving course from that and obviously saving the carbon dioxide and all the waste components there as well. We start with a small component. We can see the benefit. If we extend it, these savings and the reductions of carbon emission is huge. And I think that’s what we need as well to help achieve the net zero target by 2050.

In a conservative industry that is risk averse, is there government policy that would support the uptake of low carbon technologies like CO2 Concrete? And what is it that you would like to see exactly in terms of policy?

Oh, I would really love to see that there’s a policy surrounding recycled products. At the moment standards are only available for concrete in general. That most of the time is virgin concrete from the industry point of view. If they see a guideline, that is available for recycled concrete or recycled aggregate and it hasn’t been updated for the last 20 years and the market has changed a lot, but that standard hasn’t been able to improve. They are still limited to 20 to 30 per cent recycled aggregate replacement for low grade application such as pavement. They’re still limited on those, but I have to say technologies are around CO2 Concrete technologies is one of those. We can actually reuse the recycled product much better than what we believe. But the standards are not there. And because of the conservative industry, they may step back for a little bit and see how we go first. And for me, I would really love to see a standard to be able to implement recycled concrete and of course, CO2 Concrete as well.

Are there global examples of low emissions construction technology that you would like to see replicated in Australia or indeed any policies that you would like to see replicated in Australia?

Yes, I’ll give an example in Japan. Japan is very similar to Hong Kong. It’s a very densely populated country. They have nowhere to put landfill and they also have no natural resources. That’s the reason that they actually enforced a policy that they have to use recycled concrete if the building is of a certain size. And that’s where at that stage, basically all the Japanese industry are finding ways to use recycled concrete because they have to. And that’s where the trick is with them as well. And I have to say for recycled concrete, Japan is one of the major leaders in that.

This is an interesting case study of how you can take an innovation from a lab in a university and out into industry. How did you cross that valley from the lab to the market?

I have to say that is very difficult and is also very time consuming and is also a lot of heart break as well. Because when you spend a lot of time in the laboratory, you know that it is good, but the market is not accepting it. We are going through a different kind of journey, different kinds of approaches, and still questions come back and we can discuss those questions. But the thing is, how can we really be able to give that confidence to start using it? It’s a really difficult journey and it’s still difficult at this stage.

And what are the next steps for CO2 Concrete?

Yes, next step for CO2 Concrete is we definitely want to see the product out in the market, really going to the full commercialisation scale. And we are really looking forward to that. And what we need is to look for partners to support the product development. We will be interested to talk to any recycled aggregate companies and also concrete companies to see where we can go next. Because CO2 Concrete is targeting concrete waste, the situation at the moment is there’s a lot of mixed waste. When we crush the building, the building always is mixed. That is also difficult for the contractors to send the clean concrete waste to recycling plants. Although they have reduced the landfill costs, but they are still a kind of an investment in terms of the sorting and what I’m looking into, the next project that I’m currently working on for the next four years is to look into a way to recycle the mixed aggregates.

I understand that earlier on you also had a mentor that was vital to your journey. How vital is the role of mentorship in science and technology, and how did that influence the way that you teach and the way that you conduct your research?

Mentorship is very important because for myself, in my experience, if I didn’t have my mentor in my undergraduate studies, I don’t think I would have pursued research. I may [have] just continued working in industry because that’s what all of us as undergraduate students [did] at that time, they all go to the industry. Working as surveyors, engineers, they are all working like that. And this – no one really thinks about research and theoretically, we don’t know what research is. My mentor actually was able to give me support and also help me to understand what research value come from. And that’s actually where I start researching when I was at undergraduate studies. And that’s what I also designed to continue my education as PhD afterwards as well.

Okay, it’s a lot to look forward to, Vivian Tam. Could you please all join me in thanking Vivian for her time today? To follow the program online you can subscribe wherever you get your podcasts. And visit the 100 Climate Conversations exhibition or join us for a live recording, go to 100climateconversations.com.

This is a significant new project for the museum and the records of these conversations will form a new climate change archive preserved for future generations in the Powerhouse collection of over 500,000 objects that tell the stories of our time. It is particularly important to First Nations peoples to preserve conversations like this, building on the oral histories and traditions of passing down our knowledges, sciences and innovations which we know allowed our Countries to thrive for tens of thousands of years.